1. Field of the Invention
This invention relates in general to elevator systems, and more specifically to new and improved arrangements for preventing the doors of an elevator car from being forceably opened when the elevator car stops outside a predetermined allowable displacement zone from a floor level.
2. Description of the Prior Art
In certain instances, an elevator car may stop for an unscheduled length of time, displaced from a landing or floor. This may occur due to the failure of the electrical power supplied to the building, or because of an occurrence which triggers an emergency stop of a moving elevator car. While the doors of the elevator car will not automatically open when the car is still outside the landing zone, passengers may attempt to force the doors open, against the frictional retarding force of the door operating mechanism. While the doors may be mechanically locked, such as when the car starts a run, and mechanically unlocked at floor level, such as by a cam located at each floor which unlocks and locks the lock mechanism on the car, this presents many problems. If the car is close enough to a landing that egress may be safely made, it would be undesirable to lock the doors and prevent passenger exit. This is especially true during a general power outage, which would unduly delay authorized personnel from attending each elevator car, because of the number of elevator cars which may be so stranded. Also, even when outside the landing zone, a slight opening of the car doors for ventilation purposes is beneficial, as long as the doors do not open to the extent of permitting passenger exit. Still further, there are certain times when mechanical door locks are completely undesirable. For example, firemen use elevator cars to take equipment close to the floor of a fire, with the firemen placing the car in a firemen's mode, using a keyed switch, which allows them to have more complete control over the operation of the car and its doors. A mechanical lock of the car doors outside the landing zone would thus be undesirable. Other instances where mechanical door locks would be undesirable are during a hospital emergency mode, and when the elevator car is operated by maintenance personnel on "hand" control.
Thus, it would be desirable to provide a door lock for an elevator car which provides positive restraint against unauthorized door opening outside the landing or leveling zone, but which has the flexibility of accommodating those instances when locking is undesirable.